To characterize brain morphologic changes in normal development from ages 4 to 18 and o provide a contrast group for clinical populations to examine developmental hypothesis of neuropsychiatric disorders we are acquiring and MRI data base of healthy children and adolescents. Analysis indicates enormous variability of brain volumes highlighting the need for large samples and longitudinal study designs, which are underway. Using this normative data, a study of children with sydenhams chorea shows a highly significant selective increases in the volume of caudate globus pallidus and to a lesser extent, putamen. There is no increase in thalamus or frontal lobes demonstrating the specificity of the abnormality in Sydenham's chorea. Childhood Onset Schizophrenia (psychosis before age 12) manifests several striking abnormalities, including smaller brain size (9%) and larger caudate nuclei and globus pallidus. Other findings, such as left ventricular enlargement and left anterior temporal lobe decrease, appear similar to that seen in the later onset disorder. ADHD boys exhibit smaller brain volume (6%) and abnormal development of basal greater than left asymmetry. The importance of basil ganglia development for child psychiatry is just being appreciated, and the specificity of these abnormal developmental patterns is under study. An 015 pet study of adult males with developmental dyslexia shows decreased activation for phonologic tasks. Improvement is related to activation by orthographic processing.